Servo systems are utilized for various purposes including, for purposes of illustration, aircraft instrument control and antenna positioning and control. Closed loop control (feedback) of servo motor position and/or speed is a function common to all such systems. Servo system feedback parameters vary in form. For example, position feedback may be a D.C. signal, an A.C. error signal or a digital position signal from an encoder. Rate feedback may come from the servo system tachometer feedback signal, with the phase of the tachometer signal indicating direction of rotation of the servo motor. Limit switches are monitored to indicate an end-of-travel position.
Servo motor coefficients change and motor excitation frequencies vary. Some motors require a phase shift between the excitation voltage and a reference voltage.
The servo loop processor of the invention is used in association with a central processing unit (CPU) and appropriate input/output circuitry to achieve the aforenoted closed loop control. Servo loop parameters as well as servo motor speed and/or position are downloaded from the CPU to the servo loop processor. The downloaded information and servo loop feedback parameters are used for determining an appropriate output level and phase for driving the servo motor.